Grindstones are used in grinding units, whereby not only the grindstones but also a workpiece to be ground revolve during grinding operation. The shape of the grindstones varies depending upon the face and position of a workpiece to be ground. For example, cylindrical surfaces are ground with the faces of revolution of grindstones formed into the disc shape, while flat surfaces are ground by rotating a plural number of rectangular grindstones being arranged in a circle in such a manner that grinding may be effected with an end face of each grindstone.
Regarding the shape of grinding units to be mounted on a grinding machine, in the case of cylindrical grinding, disc grindstones are fixed by a holder and mounted on a grinding wheel spindle, whereas in the surface grinding operation, a plural number of rectangular grindstones are fixed on the circumference of a rotary cylinder attached on the wheel spindle.
FIGS. 4(A), (B) and (C) are a front view (in part) and sectional view and a partly enlarged perspective view illustrating a conventional grinding unit mounted around a cylinder of a grinding machine. Rectangular grindstones 27 are set to a cradle 29 of a cylinder 12A, and wedge-formed metal fixtures 30 are inserted between the two adjacent grindstones 27. When locking bolts 32 are fastened, the wedge 31 is moved toward the center of the cylinder (along the direction of the arrow), while the grindstones 27 are simultaneously forced away right and left, thereby causing the gaps to be narrowed to effect fixing.
All of the rectangular grindstones 27, which are interrelated with the metal fixtures 30, get positioned only after fastening of the locking bolts 32 of the metal fixtures. The number of grindstones mounted on the large-size grinding tool amounts up to 50 or so, and it requires a lot of time and labor to set all of so many grindstones in position, followed by fixing with wedge-shaped fixtures. Such tedious work adversely affects the rate of operation of a grinding machine in question and is undesirable. In addition, the face of each metal fixture protrudes beyond the surfaces of the grindstones, and inevitably interferes with metal fixtures 26 of a workpiece to be ground (refer to FIG. 3).
Since the rectangular grindstone 27 is not resistant to shock, adequate care is required when handling such grindstones. As wear advances, furthermore, such grindstones become difficult to be fixed with wedge-type metal fixtures, if they are oversized relative to the metal fixtures used. In light of the fact that raw materials for grindstones are costly, a method of using grindstones in a non-efficient manner pushes up the machining costs and is undesirable.
FIG. 5 is a side view illustrating the state of use of another conventional grindstone in grinding a boss 25a of a disc brake 25. A rectangular grinding unit 27A consisting of angled grindstones 2A bonded to the tip of a grindstone holder 3A are mounted around a rotary cylinder 12A of a grinding machine 11A by use of wedge-type metal fixtures. The angled tip of grindstone 2A that brings about variations in thickness tends to break off, resulting in severe damage to the service life of grindstones 2A.
When the outer face of the wedge-type metal fixture 30 (see FIG. 4), which protrudes beyond the outer face of the grindstone 2A, approaches to a metal fixture 26 of the disc brake 25, their mutual interference (i.e. collision) is inevitable depending upon the positional conditions of the wedge-type metal fixture 30. For this reason, the grinding unit 27A is slanted when used, as shown in FIG. 5.
The object of the present invention is to provide a grinding unit and a method for mounting the grinding unit that have solved the above-mentioned problems.